The present invention relates to new calixarene derivatives and the preparation method and use of said derivatives to extract actinides and lanthanides.
More specifically, it relates to calixarenes comprising a phosphinoxide-acetamide substituent, offering beneficial properties for the extraction of actinides and lanthanides, particularly trivalent actinides and lanthanides.
Therefore, said new calixarenes may be used to extract actinides and lanthanides present in aqueous solutions such as aqueous effluents from used nuclear fuel reprocessing installations or used nuclear fuel dissolution solutions.
The use of macrocyclic ligands such as calixarenes comprising a phosphinoxide-acetamide substituent, to extract metals such as lanthanides and actinides from aqueous solutions has already been envisaged, as disclosed in WO-A-96/23800 [1].
In said derivatives, the phosphinoxide-acetamide substituent is arranged directly on the phenyl cycles of the calixarene and said phenyl cycles are also substituted by alkoxy groups, for example of 5 to 18 carbon atoms.
Calix[4]arenes-bis-rings comprising two ether-ring links between two opposed benzene cores 1 and 3, and 2 and 4 are also known from the document FR-A-2 698 362 [2]. Said substances are particularly useful for the selective extraction of cesium.
Although the efficiency of said calixarenes in the extraction of actinides and lanthanides or caesium is satisfactory, research was continued to improve the performances of calixarenes in the extraction of trivalent actinides and lanthanides.
The present invention relates to new calixarene derivatives comprising a phosphinoxide-acetamide substituent which offer improved performances in relation to the calixarenes described in documents [1] and [2].
According to the invention, the calixarene complies with the formula: 
wherein R1 and R2, which may be identical or different, are alkyl, alkoxy or aryl groups, and n is an integer equal to 2, 3 or 4.
In this calixarene, the presence of ether-oxide links between adjacent benzene cores makes the structure of the calixarene rigid and more efficient in the extraction of trivalent actinides and lanthanides.
In formula I given above, R1 and R2 may be alkyl, alkoxy or aryl groups. The alkyl and alkoxy groups may be linear or ramified, preferentially comprising 1 to 18 carbon atoms. The aryl groups that may be used for R1 and R2 are monovalent groups derived from an aromatic or heterocyclic core by removing a hydrogen atom from one of the carbon atoms of the cycle. Examples of such groups include phenyl, naphthyl, pyridyl, thiophenyl and substituted phenyl groups.
Preferentially, R1 and R2 each represent a phenyl group or an alkoxy, for example ethoxy, group, where R1 represents the phenyl group and R2 represents an alkoxy, for example ethoxy, group.
The calixarenes according to the invention may comprise 4 to 8 phenyl cycles. Preferentially, the calixarene comprises 4 phenyl cycles (n=2).
The calixarenes according to formula I according to the invention may be prepared using a method comprising the following steps:
a) nitration of a calixarene according to the formula: 
xe2x80x83wherein R3 represents an alkyl group and n is as defined above, to obtain the nitro derivative according to the formula: 
b) reduction of the nitro derivative according to formula III into an amino derivative according to the formula: 
c) reaction of the amino derivative according to formula IV with a phosphinoxide acetate according to the formula: 
xe2x80x83wherein R1 and R2 are as defined above, and R4 represents the p-nitrophenyl or 2,4 dinitrophenyl group.
The phosphinoxideacetate according to formula V used in the final step may be prepared using alkyl phosphinite corresponding to the formula: 
where R1 and R2 have the correspondences given above and R5 is an alkyl group comprising 1 to 4 carbons, by reacting said group with ethyl bromoacetate, followed by hydrolysis and esterification of the acid obtained with nitrophenol or dinitrophenol.
According to an alternative embodiment, the calixarenes according to formula I wherein R1 and/or R2 are an alkoxy group, may be prepared using a method comprising the following steps:
a) nitration of a calixarene according to the formula: 
xe2x80x83wherein R3 represents an alkyl group and n is as defined above, to obtain the nitro derivative according to the formula: 
b) reduction of the nitro derivative according to formula III into an amino derivative according to the formula: 
c) reaction of the amino derivative according to formula IV with bromoactyl chloride according to the formula:
BrCH2COClxe2x80x83xe2x80x83VI
xe2x80x83to obtain the calixarene derivative according to the formula: 
d) reaction of the derivative according to formula VII with a phosphonate or phosphinate according to the formula:
R1xe2x80x94Pxe2x80x94(R2)2xe2x80x83xe2x80x83VIII
xe2x80x83wherein R1 is an alkyl, alkoxy or aryl group and R2 is an alkoxy group.
The calixarenes according to formula I of the invention may be used to separate at least one metal selected from actinides and lanthanides present in an aqueous solution, such as dissolution solutions and aqueous effluents from used nuclear fuel reprocessing installations.
The aqueous solution may be a nitric solution containing 1 to 4 mol/l of HNO3.
To carry out this separation, the aqueous solution containing the metal(s) to be separated is placed in contact with a non-miscible phase comprising at least one calixarene complying with formula I given above, to extract the metal(s) in the non-miscible phase.
Said non-miscible phase is generally composed of a solution of the calixarene(s) according to the invention in a suitable organic solvent.
Examples of solvents that may be used include alkyl benzenes and nitrophenyl alkyl ethers.
Preferentially, an ether such as ortho-nitrophenyl hexyl ether is used as the solvent.
The calixarene concentration of the non-miscible liquid phase particularly depends on the solvent used. Concentrations ranging from 5.10xe2x88x925 to 10xe2x88x923 mol/l, for example a 10xe2x88x923 mol/l concentration, may be used.
To implement the separation method according to the invention, the aqueous solution may be placed in contact with said non-miscible liquid phase in conventional liquid-liquid extraction installations such as mixers-clarifiers, centrifugal extractors, pulsating columns, etc., but also by means of supported liquid membranes.
The supported membrane technique consists of immobilising the non-miscible liquid phase on a solid substrate such as polypropylene. Using this technique, it is possible to transfer the metals to be separated from the aqueous solution in which they are contained into an aqueous re-extraction solution. In this case, one of the sides of the membrane is in contact with the first aqueous solution containing the metals to be separated and the other side is in contact with an aqueous re-extraction solution.
The substrate of the supported liquid membrane may be a microporous membrane wherein the pores are filled with calixarene in solution in a suitable organic solvent. Said microporous membrane may be made of polypropylene, polyvinylidene fluoride or polytetrafluorethylene. Said membrane may be used as a separation between a first compartment with the aqueous solution containing the metals to be separated and a second compartment with the aqueous re-extraction solution.
To obtain satisfactory extraction with supported liquid membranes, it is advantageous to use thin, highly porous membranes with a small pore diameter. Said membranes may be used in the form of modules such as plane membrane or hollow fibre ultra- or microfiltration modules, used to process high fluid flow rates.
After the extraction of the metal(s) to be separated in the non-miscible liquid phase, they may be recovered by re-extraction in an aqueous re-extraction solution. Said solution may be an aqueous complexing agent solution. The complexing agent may be an organic acid or an organic acid salt such as methylene diphosphonic acid, oxalic acid, citric acid, oxalates and citrates. The use of such solutions makes it possible to obtain the re-extraction of separated metals with high yields.
The invention""s other characteristics and advantages will be seen more clearly on reading the following examples, which are naturally given as an illustration and are not exhaustive, with reference to the appended figures.